Oh, Thanks. When I was a child I asked all the adults around about this, but they looked at me like I were a lunatic, so eventually I just stopped talking about it.... :) Glad to have an answer now.
I learned to do this as a child because I always had issues with feelings of pressure in my ears. I was so sensitive that riding up or down a hill that was big enough would cause discomfort.
What is responsible for this?
I don't know how I discovered how to do this but it always seemed natural.